A Congruence Conjecture of Z.-W. Sun for Reciprocal Central Binomial Sums

Source abstract

Let $p>5$ be a prime. We prove a conjecture of Z.-W. Sun asserting that $\sum_{k=1}^{p-1}\frac{1}{k^4\binom{2k}{k}} \equiv \frac{H_{p-1}}{p^3}-\frac{7}{45}pB_{p-5}\pmod{p^2}.$ As a consequence, we obtain $\sum_{k=1}^{p-1} \frac{H_{k-1}^{(2)}}{k^2\binom{2k}{k}} \equiv \frac{H_{p-1}}{3p^3} +\frac{26}{135}pB_{p-5} \pmod{p^2},$ an equivalent conjecture of K. Hessami Pilehrood and T. Hessami Pilehrood. Here $H_n^{(m)}$ denotes the generalized harmonic numbers of order $m$, with $H_n=H_n^{(1)}$, and $B_n$ denotes the $n$th Bernoulli number. The proof combines $p$-adic congruences involving harmonic numbers, finite-sum identities, and complex residue calculations via the residue theorem.